Pictured is my test set up . I used two ( Three
actually ) USB wall
adapters , the one in the picture being advertised as being a 1A model .
The other USB adapter was advertised as being 2A , interesting little
tidbit , each adapter is capable of supplying half the advertised
current . Also I am using a Charge Doctor to monitor the current
going to the charger . So with the 1A adapter that equals around half an
amp , and with the 2A adapter about one amp of current . So that means I
have a way of limiting current going to the USB charger .

2A adapter ( 1A
actual ) Here we have all of 5watt to play with . Depending
on the voltage state of the battery being charged , you could very well
pump 5Watt into the charger ( less any losses ) . If you do your math ,
that is a potential charge rate of around 4+ Amps ( depending on how
much power is absorbed by the charger ) and the actual voltage state of
the battery . ( Yikes ! ) I did have a battery ( old ) that had a
resting voltage of 0.6v , and I did use the 2A adapter and it did hit
0.97A on the Charge Doctor ... Single battery charge ( Yes it did
charge quickly )

1A adapter ( 0.5A
actual ) This is much better in my humble opinion as we
have some 2.5Watt to play with . Even with half as many watt's to
play with the potential is there to charge a single AA at potentially
over 2A .. Charging 2 to 4 AA would make much better sense . I am
rather sure one of my USB wall adapters does 0.25A , and I would be much
happier using that ( 0.25A ) , especially if I only had one or two
batteries to charge .

0.5A adapter ( 0.25
actual ) This is again a better option if only charging one
or two batteries as we only have 1.25Watt to play with . This means we
have about a 1A maximum charge rate for a single battery , and half that
for two and half again as much for 4 . It's good to have a half
dozen USB wall adapters .

Charging

This is a small charger , and on receiving and
opening the package I was a little surprised at just how small and light
this charger was . At just under 8cm long and just over 4cm wide and
weighing next to nothing , I wasn't sure how well it would work or how
long it would work . Well I have been put in my place I have to tell you
. For such a small light FAST Charger , the first thing to amaze me was
the lack of overcharging . And the second thing to amaze me was the lack
of heat , the charger actually runs cool . Even @ 5 watt's , only the
batteries get warm , the actual charger remains cool . Now I am not sure
if the charger actually terminates or trickle charges on completion . At
the moment I have no way of getting probes into such a small space to be
able to monitor what is going on , but I will remedy this by making a
dummy battery that is connected to an actual battery ( AA or 14500 ) and
has a Amp meter and voltage meter in the circuit ( This will be in the
future - perhaps weeks depending on EBay sellers )

The charger has little lights over each battery
bay , and these blink slowly ( at the start ) and then quickly as you
near the end . And on completion they should be a solid light , but
depending on the battery ( condition ) the voltage may not reach a point
where the lights stop blinking , so the charger may be trying to reach a
certain voltage state ( ? ) This is why I use a Charge Doctor , It shows
the current going to the charger , and when it reaches 0.01/0.02A , I
know the batteries are done and there is no need to rely on blinky
lights . ( If you charge VIA USB - you really want a USB Charge
Doctor )

To be honest I am not a fan of fast charging
batteries , but at least with USB chargers you do have some control of
just what USB power source you plug your USB charger into . Thus
allowing you to control the charge rate , and if you have a Charge
Doctor then you can monitor your charger on the fly .

Power Bank

Pictured is the Z15 being used as a powerbank to
feed a small Xtar charger with a 16340 . The instructions are in Chinese
, so I believe all 4 batteries are being used to power any device . So
with 2000mAh AA batteries , this could very well be a very small 8000mAh
powerbank . The experiment I want to try is how many batteries are
needed to Bank with ? And the answer is all 4 . 3 - 2 or 1
battery installed = no Banking available . Hmmm 4 x 1.5v or should that
be 1.4v fully charged nimh , = 5.6v . So at what voltage does charging (
powerbank ) end ? 5v or maybe 4.2v ...

It's bad news folks , looks like the bank closes
at 5v , and that means there is not that much power available to charge
a device with or to power a device . At best it might work for a short
time as an emergency power supply for your phone or USB device . (
depending on power demands ) If you were to throw in some Lithium or
Alkaline batteries ( ? ) , as they have a higher nominal voltage , you
may be able to have a longer lasting powerbank . I did throw in some
Alkalines @ 1.6v to see if they would work for the powerbank mode
........ and ....... yes it works . So a little
disappointing the 5v cut off as it does not utilize the nimh batteries
to their full potential . ( Nor any other AA battery - possibly Lithium
could be ok ( ? )

Last Word

Would I recommend this charger to joe six pack ?
........ not really !

I would how ever recommend this charger to
anyone who is an enthusiast ( has a clue ) . If you use this charger
intelligently , then it has the potential to be a great little charger .
I was amazed myself how small , light and how cool it ran even at what I
would call high current for AA charging . It could be used in a car VIA
a sigaret lighter USB adapter , or powered by a solar panel ( due to the
current potential , I would not connect it to a Computer USB port ) .
The charger is insanely light weight so could be great for back packing
.

It is a fast charger , there is no doubt about
that . So if you are a fan of such then you really should take a look at
the Xiaomi Z15 AA/AAA USB charger .. It works , it runs cool and it
recharges batteries . It worked for me ( I like it ) only because I have
half a dozen USB wall adapters of varying current capability allowing me
to change the nature of the beast ( tame it so to speak ) .

The powerbank feature (?) a little disappointing
with the 5v cut off , but could - would - should work better with
Alkalines or Lithium ( possibly ) . The question I keep asking
myself is , could it be better for the asking price ( $10 USD ) , and I
just don't see it . The Z15 would need to be completely rebuilt on a
larger body ( possibly ) to incorporate some sort of boost circuit to
maintain 5v for the battery bank . That's more parts , a re design ,
more money to build and would be an entirely new product . So I can only
conclude the Z15 is pretty much all it can be , and for anyone reading
this the question would be is it enough ! Does it do what you want ? (
For $10 USD )

To date I have charged over 40 batteries ,
amazing considering the short time ( 3 days ) I have been playing with
the charger . I would seriously recommend a USB wall adapter that
limits current to 0.5A or 0.25A if you plan on using the Z15 as a
primary AA charger . Especially if you charge one or two batteries at a
time , as prolonged high current charging may shorten battery life .
For occasional or emergency charging the Z15 will do the job extremely
well , and I can see this charger connected to a Solar panel .
There are applications where this charger could be the bees knees and it
does perform as advertised .

I would like to thank
Gearbest for allowing me to test this
charger ..